I'm so sorry to hear about Snickers. I feel for all of you more than you can possibly imagine.
Your vets are talking through their fundaments if they are giving you a runaround like this over running diagnostics for pancreatitis. As others have advised above, the SNAP fPL or Spec fPL tests give results really quickly (SNAP gives yes/no result; Spec gives numeric result which can be a guide to severity).
I also recommend ondansetron for nausea (although Cerenia may help more with vomiting). The standard dose is 1mg twice a day, although Saoirse gets 2mg twice a day (10lb/4.5kg body weight).
Keep a log of how frequently Snickers poops and also do fecal exams to check firmness and colour of stools; constipation - even when mild - can cause lethargy, major discomfort, vomiting, and low mood (if Saoirse is any benchmark). As Elise suggests, pumpkin can help but introduce it very gradually; it doesn't agree with all cats. Psyllium husk is another fibre source but if you try this use it very sparingly as it can lead to very big poops on trace amounts. More info at
felineconstipation.org.
Useful links for pancreatitis (and kidney-related nausea issues):
Nausea symptoms and treatments
IDEXX Pancreatitis Treatment Guidelines
If gut motility is a problem then brief treatment with metoclopramide (Reglan) can help to get things moving. (Doesn't do much for non-constipation-related nausea problems as cats don't have many of the receptors it targets and prolonged use can cause irreversible nervous-system-related side effects).
I hope things improve very soon for all of you and, based on your comments above, I think the smart money is on getting Snickers seen by a different vet.
Mogs
EDITED BST 14:35 Sunday 17 July - added hyperlinks.
(My head is an absolute mess at the moment; sorry I didn't put the links in last night.)
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